What Are The Different Sedimentary Rock Types Based On Grain Size, From Small To Large?

This basics page focuses on sedimentary rocks, which are sediments that were turned into solid rock by geologic processes. Sedimentary rocks contain data near what was occurring on earth's surface at the place and time the sediments were deposited. In some cases sedimentary rocks incorporate fossils, which provide data virtually what was living at a certain identify and time on world.

There are ii main groups of sedimentary rocks: chemical and clastic. Clastic is sometimes called detrital. Each type of sedimentary rock is formed when sediments lithify (turn into rock). Chemical sediments are sediments that precipitate from solution, for example salt crystals that abound at the bottom of an evaporating body of h2o. Clastic sediments are solid pieces of weathered and eroded rocks or minerals, for example sand on a beach.

This folio provides the background needed to empathise the terms used in the sedimentary rock classification table at the end of this folio.

Lithification—Sediments to Sedimentary rocks

Sedimentary rocks are rocks made of lithified sediment. Sediments are grains of rocks, minerals, or mineraloids deposited on the surface of the earth. Reflect on the rock cycle for an indication of the relationships between the rocks that erode to become sediments and sedimentary rocks. For sediment to get sedimentary rock, it ordinarily undergoes burial, compaction, and cementation.

Clastic sedimentary rocks are the issue of weathering and erosion of source rocks, which turns them into pieces—clasts—of rocks and minerals. Once they get pieces, these clasts are free to move away from their source rock and they ordinarily do. They are most often transported past water and deposited as layers of sediment.

The burial stage of lithification involves the deposition of more sediment layers top of those that had been deposited earlier. In a sedimentary bowl where sediment is being deposited, it is common for subsidence (lowering) of the basin to be taking place, either considering the crust and lithosphere beneath it are subsiding into the drape to some extent, or because the surrounding uplands are undergoing uplift relative to the basin, or both. This allows thousands of feet of burial, in some cases tens of thousands of anxiety of burial, to occur.

As sediments are buried, the weight of overlying fabric exerts pressure level, causing compaction of the sediments. The pressure, known as lithostatic pressure, "squeezes" the sediments from all sides into a smaller volume. Lithostatic pressure level packs the sediment grains closer together and reduces the porosity – space between the sediment grains.

Some chemical sedimentary rocks are rock as soon every bit the sediments accept been deposited by crystallization of minerals from substances dissolved in h2o, at the world'southward surface. Examples include stone salt and other evaporite deposits. These sediments of salt crystals and other minerals course sedimentary stone without having to undergo burial and compaction.

During burial and compaction, sediments will undergo some amount of cementation. Cementation refers to the growth of new minerals between the sediment grains. These new minerals bind the sediment grains together. One form of cementation is growth of quartz rims on the surfaces of pre-existing quartz grains in the sediment. This new mineral growth is a consequence of h2o in the pore spaces that dissolves and precipiates quartz. A second mutual cementing mineral is hematite, a red or rust-colored atomic number 26 oxide mineral, which precipitates onto the sediment grains from a combination of dissolved atomic number 26 and oxygen from water in the pore spaces. A third common cementing mineral is calcite, which also precipitates from ions dissolved in the h2o in the pore spaces during lithification. Although there are other cementing minerals, quartz, hematite, and calcite are mutual cementing minerals that grow between or on the surfaces of the original sedimentary grains.

Generalized steps from source to sedimentary rock:
weathering >> erosion >> ship >> deposition >> burial >> compaction >> cementation >> sedimentary stone

Minerals and Sedimentary Rocks

Any type of rock containing any type of mineral will undergo weathering and erosion at the earth's surface. However, some minerals are more than stable than others in earth'southward surface environments and are more than likely to be plant in sedimentary rocks.

Grains of clastic sediment, which are chosen clasts are winnowed and modified during the weathering-to-degradation process. Weathering of minerals volition gradually eliminate the physically weaker and chemically more reactive minerals, increasing the relative abundance of more resistant minerals. Quartz tends to become increasingly abundant during the process, due to its common occurrence in the source rocks combined with its hardness and lack of cleavage, which makes information technology resistant to breaking down physically. Quartz is not hands dissolved or chemically altered, then information technology is resistant to breakdown by chemical reactions equally well. That is why beach sand is oft more rich in quartz than any other mineral. Sediments rich in quartz are considered mineralogically "mature" because they have been subjected to a longer interval of physical and chemical modification during the erosion-to-deposition process. Mature sediments are deposited further from their source rocks in space and/or time than immature sediments.

Feldspars are the most common type of mineral in world'south crust and are besides arable in many clastic sediments and sedimentary rocks. Although feldspar is a fairly hard mineral, it does carve (split apart) and is chemically reactive, peculiarly in the presence of water. The most abundant product of chemical reaction of feldspar and water is clay minerals. During the erosion-to-deposition process, clastic sediments lose feldspar and gain a larger proportion of clay. Other minerals such equally amphiboles, micas, and carbonates are relatively soft and chemically reactive and tend to be scarce or absent as sediment grains in mature clastic sediments, although calcite may be nowadays in clastic sedimentary rocks as a secondary, cementing mineral that grew during lithification.

Minerals in chemic sedimentary rocks precipitate from water and usually remain in place or are not transported far earlier lithification. Such mineral sediments are subjected to little, if any, erosion and transportation. Therefore, the minerals in chemical sedimentary rocks are non winnowed during the weathering-to-deposition process every bit are the minerals in clastic sedimentary rocks. In some cases, during the formation of chemical sediments, the minerals may change as a result of chemical reactions. For example, dolostone is a chemical sedimentary stone that forms in sure coastal environments past amending of precipitated calcite to dolomite.

Besides minerals, mineraloid solids occur in some chemic sedimentary rocks. For example, the carbonaceous material in coal is an organic mineraloid rather than a mineral. Some other example, opal, is a chemic sedimentary rock that does not have a fully developed crystal lattice and therefore is a mineraloid.

Sedimentary Stone Textures

In clastic sediments the sedimentary texture includes the grain size, rounding, and sorting of the grains, all of which are related to what happened to the sediment during the weathering-to-degradation process.Because the processes that atomic number 82 to the formation of chemic sedimentary rocks do not involve the conditions-to-deposition procedure, there is no widely agreed-upon texture scheme that applies to chemical sedimentary rocks.

Clastic textures

Clastic sedimentary textures are described in terms of the size of the sediment grains, how round they are, and how well they are sorted.

Grain size

The diameter or width of a clastic sediment grain determines its grain size. Specific ranges of grain size have specific names.

Gravel is an overall proper name for large sediment grain size, which includes boulder, cobble, and pebble.
Sand includes sediment grains ranging in size from 2mm to 0.625 mm.
Silt is the name of a sediment grain that range in size from 0.625 mm to 0.0039 mm.
Mud is the smallest grain size and is also known as clay. It is of import to distinguish the grain size called clay from the mineral called clay. Clay sized grains are as well pocket-size to see individually without the assist of a microscope.

Rounding

Clastic sediment grains can exist round, angular, or in-between (subangular or subrounded). Breccia is a clastic sedimentary stone that by definition consists largely of angular grains of pebble size or larger. Conglomerate, another sedimentary stone, consists largely of rounded grains of pebble size or larger. The schematic diagram below shows classes of rounding, from the left: angular, subangular, subrounded, rounded. Not shown are very angular and well-rounded, which are less common.

schematic diagram of four classes of rounding showing angular, subangular, subrounded, and rounded.

Sorting

The extent to which all the grains are the same size is known as sorting. If all the grains are the same size, they are well sorted. Some sandstones are well sorted, and some are not. Most conglomerates are poorly sorted, and consist of a mixture of grain sizes ranging from sand to pebble. The schematic diagrams below stand for poorly-sorted, moderately-sorted, and well-sorted sediments.

schematic diagram of poor sorting schematic diagram of moderate sorting schematic diagram of well sorted

Other Aspects of Texture

Other aspects of clastic sedimentary texture include the packing of the grains, the porosity of the stone, and the hardness of the rock as a whole.

The packing of the grains applies only to poorly sorted sediments in which the effectively clasts form a matrix around the coarser clasts. If the large grains are touching each other, the packing is said to exist clast-supported. If the coarse grains are separate and non touching each other, with the finer-grained sediment between them, the packing is said to be matrix-supported.

The porosity of a rock or sediment is the amount of empty infinite betwixt the grains of sediment.

The hardness of the stone refers to how easily it breaks apart. Shale is harder than claystone, for example.

How to Place Sedimentary Rocks

Clastic

The common names of clastic sedimentary rocks—conglomerate, sandstone, siltstone, and shale—are based solely on grain size. Still, there are more precise names within these broader categories that are based on clastic sediment features other than grain size. Breccia is a clastic sedimentary rock distinguished from conglomerate past the angularity of its clasts.

A clastic sedimentary rock only made of sand-sized grains qualifies as sandstone, regardless of what minerals the grains are made of. More complete names for diverse sandstones are based on their mineral composition. Some sandstones are made nearly entirely of quartz. Sandstone made well-nigh entirely of quartz is chosen arenite. Other sandstones take lots of feldspar mixed with quartz. Such sandstones are chosen arkose. Other sandstones are a mixture of feldspar, quartz, dirt, and pocket-size fragments of "lithics," nighttime-actualization minerals and rock fragments, which represent mineralogically young sediments. Such sandstones are technically known as lithic wackes, although geologists often telephone call them by their quondam name, graywackes, and the rocks are sometimes informally described as "dirty sandstones."

In using the sedimentary rock classification table that accompanies this department, y'all will see that the clastic sedimentary rocks are classified on the basis of grain size. Sandstones are rocks made of sand-size grains. Shale is layered sedimentary rock fabricated of fine mud-size grains also small to see with the naked heart.

Chemical

The key to naming chemical sedimentary rocks is the minerals from which they are made. For case, all limestones consist generally of the mineral calcite. Coal is made of carbon. Stone salt is made of salt minerals such equally halite. Gypsum rock is made of the mineral gypsum. Chalcedony is fabricated of microcrystalline quartz, quartz grains so tiny that they cannot exist distinguished even with a standard optical microscope.

Settings for the Origin of Sedimentary Rocks

The minerals, textures, structures, and fossils in sedimentary rocks are used to infer what was happening on earth biologically, chemically, physically—in sum geologically—at the time and place the sediments were originally deposited.

Sedimentary Rock Classification

*Clastic Sedimentary Rocks*
Grain Size	Rounding	Sorting	Rock Name
gravel fibroid (> 2 mm)	angular	poorly	breccia
gravel fibroid (> 2 mm)	rounded	poorly	conglomerate
sand medium (0.0625–two mm)	variable	variable	sandstone
	rounded to subangular	well to moderately	quartz arenite— >90% quartz
	subrounded to angular	well to moderately	arkose— >25% feldspar
	subangular to athwart	moderately to poorly	graywacke—high % lithics, clay matrix
silt fine (0.004–0.0625 mm)	variable	well	siltstone
clay actress fine (< 0.004 mm)	not visible	well	shale—breaks forth bedding planes
			mudstone—lacks bedding planes
			claystone—pure mineral clay, very soft
*Chemical Sedimentary Rocks*
Mineral	Distinguishing Characteristics	Rock Proper name	Mutual Depositional Environment
calcite	softer than glass, reacts to HCl	limestone	warm shallow sea
calcite	visible fossils, softer than glass, reacts to HCl	fossiliferous limestone	warm shallow sea
dolomite	white to pinkish, softer than glass, reacts to HCl only when powdered	dolostone	saline lagoon
calcite	grayness or brown, porous, reacts to HCl	travertine	evaporated leap or cave h2o
calcite	white, powdery, reacts to HCl	chalk	warm shallow ocean
microscopic quartz	conchoidal fracture	chert	deep ocean floor
microscopic quartz	ruby-red, conchoidal fracture	jasper	deep ocean flooring
microscopic quartz	black, conchoidal fracture	flint	nodules in limestone
microscopic quartz	translucent, layered, conchoidal fracture	agate	nodules in volcanic rocks
microscopic quartz	white, powdery	diatomite	lakes in volcanic environments
carbon	blackness, soft, low density	coal	heavily vegetated swamp
halite	tastes similar salt, cubic crystals and cleavage	rock salt	evaporating h2o body
gypsum	softer than fingernail	gypsum rock	evaporating water torso

Reflection Questions

What skill does this content help you lot develop?
What are the cardinal topics covered in this content?
How can the content in this section help yous demonstrate mastery of a specific skill?
What questions do yous have about this content?